System for the transmission of intelligence.



R. A. HEISING.

SYSTEM FOR THE TRANSMISSION OF INTELLIGENCE.

APPLICATION men OCT. 9. 1915.

1 1 99, 1 80. Patented Sept. 26, 1916.

UNITED STATES PATENT OFFICE.

RAYMOND A. HEISING, OF EAST ORANGE, N JERSEY, ASSIGNOR, BY MESNE ASSIGN- MENTS, TO WESTERN ELECTRIC COMPANY, INCORPORATED, A CORPORATION OF NEW YORK.

SYSTEM FOR THE TRANSMISSION OF INTELLIGENCE. I

Specification of Letters Patent.

Patented Sept. 26, .1916.

To all whom it may concern lie it known that 1 RAYMOND A. Ilmsmfl, a citizen of the United States, residing at East Orange, in the county of Essex and State of New Jersey, have invented certain new and useful lmprovements in Systems for the 'Ihansmission of Intelligence, of which the following is a full, clear, concise, and exact description.

This invention relates to improvements in the art of transmitting signals by means of high frequency electric waves.

Its object is to provide means for modulating the amplitude of a high-frequency wave in accordance with the wave form of a low-frequency signal to be transmitted. This object is accomplished by impressing upon one part of the divided input circuit of a thermionic amplifier a high-frequency voltage, and upon the other part of said input circuit a voltage having the wave form of the signal to be transmitted. As a result of this, there appear in the output circuit of the amplifier, under proper conditions, amplified and modulated high frequency currents which may be used to supply power to an antenna or other circuit from which the signal is to be transmitted.

The possibility of so producing a modulated high-frequency current depends upon the fact that the amplifying power of the thermionic repeater depends upon, and increases with, the voltage impressed upon its input terminals. If, therefore, a variable voltage, corresponding to the signals to be sent, is impressed upon one part of the input circuit, and if the high-frequency alternating voltage is impressed upon another part, the high-frequency power appearing in the output circuit will vary in accordance with the low-frequency signal voltage. In thus applying these two voltages, it is essential, for good quality of transmission, that the change in amplification be produced by the signal voltage, so that the latter should preferably be larger or should be applied to be more effective than the highfrequency voltage. It has been found, however, that telephonic communication may be maintained even if the condition is violated, but the quality is then somewhat impaired.

The circuit arrangement which has been found by experiment to be most desirable is that shown in the drawing, which represents a preferred form of this invention.

In that drawing, 1 represents any suitable generator of high-frequency power. It need not have a large power capacity, since it is required to furnish but a small high-frequency voltage. By means of the transformer 2, the electromotive force developed by generator 1 is impressed upon one grid 3, of the divided input circuit of a thermionic amplifier at, whose other elements are a heated cathode 5. an anode (i, and a second grid element 7.

8 represents a microphone, and 9 a battery by means of which it is supplied with direct current. The transformer 10, whose primary circuit contains the microphone, provides that a signal voltage produced in the microphone circuit shall be impressed upon the second input element 7 of the amplifier 4.

11, 11 are batteries whose objects are to insure that the electrodes 3 and 7 shall always be at negative potentials with respect to the filament 5. Under these circumstances no electrons can pass from the filament 5 to either input electrode, and therefore practically no current is taken by the input circuit.

12 is another battery which maintains the space current in the amplifier between anode 6 and cathode 5. The output circuit of this amplifier contains the coil 13, to which is coupled another 'coil 14, which, in combination with condenser 15, forms a tuned circuit whose frequency may be adjusted to that of the wave to be transmitted. The high non-inductive resistance 16 is preferably placed in shunt to the condenser 15, its object being to adjust the sharpness of tuning of the resonant circuit, and also to insure that the input circuits of the amplifiers, next to be described, shall offer a definite impedance to incoming waves.

' The amplifiers 17' are arranged in parallel and have their input circuits connected across the terminalsof the resonant circuit 14, 15, the common output circuit of these amplifiers including the coil 18. The object of these amplifiers is to produce, in the output circuit, avoltage considerably larger than that appearing over their input circuits, and it is not essential that the power output ofthis set shall be large. The resonant circuit 19, 20, also tuned to the frequency to be transmitted, is coupled to the coil 18. The input circui-ts of a number of amplifiers 22, arranged in parallel, are connected to the terminals of this second resonant circuit. The resistance 21 is added because it has been found to render more stable the operation of the amplifiers 22. These amplifiers are especially designed to produce in their output circuits high currents, rather than high efi'ective alternating voltages, and therefore the combination of impressed upon the grid 3 from the genera- 4 tor 1 are, in the absence of an electromotive force due to microphone 8, simply repeated in enlarged form as variations of current in the output circuit. When, however, an electromotive force of the signal wave form is impressed upon the grid 7, the effect of the signaling voltage is to change the amplifying power of the repeater 4:, and conse-' quently to change also the amplitude of the high-frequency current variations in its output circuit. A modulated high-frequency current is therefor produced in the coil 13, and its effects are transmitted to antenna 24 by means of the intermediate apparatus, whose operation has already been described sufiiciently in detail.

Although this invention is shown as applied to the transmission of radio signals, it is obvious that the mere substitution of a wire circuit, for example a telephone line, for the antenna 2 1, will permit the use of this system for the transmission-of modulated high-frequency Waves over Wire lines,

and I therefore desire to include that application as a part of my invention. It is also obvious that departures may be made from the particular circuit arrangement shown in the drawing.

What is claimed is:

l. The combination in a radio transmission system, of an antenna, a source of highfrequency waves, a source of waves of signaling frequency, a thermionic repeater hav-' ing an output circuit and a divided input circuit, the two parts of said input circuit being connected respectively to said sources of high-frequency waves and of low-frequency waves, of amplifying means whereby the modulated high-frequency waves in the output circuit of said repeater may be further increased in power, and a means for impressing such augmented power upon said antenna.

2. In a system for the transmission of signals by means of modulated high-frequency waves, a circuit, a thermionic amplifier having an output circuit, connected to said first mentioned circuit, and a divided input circuit; means for impressing highfrequency electric oscillations upon one part of said divided circuit, and means for impressing impulses of signaling frequency upon the other part of said divided circuit.

3. In a system for the transmission of signals by means of modulated high-frequency waves, a circuit, a source of impulses of signaling frequency, a source of oscillations of high-frequency, and a thermionic amplifier having two grid elements, one of said elements being connected to said source of impulses, the other to said source of oscillations, and the output circuit of said amplifier being so connected as to transfer power to said first mentioned circuit.

In witness whereof, I hereunto subscribe my name this 7th day of October, A. D. 1915.

RAYMOND A. HEISING. 

